Research will continue on the development of additional somatostatin analogues with improved selectivity for inhibition of glucagon, growth hormone, and gastric acid secretion which could have therapeutic value in the treatment of diabetes mellitus (particularly the juvenile form), acromegaly, gastric ulcers, and acute pancreatitis. An additional aspect of this work, which has assumed very great significance with our discovery of several competitive inhibitors of the hormone, is the investigation of their use as hormone releasing factors. Among the most important uses for antagonists of somatostatin might be stimulation of release of insulin or growth hormone. As with normal somatostatin analogues, there appear to be excellent prospects for developing selective antagonists. Synthesis of analogues will continue to be by established and new solid-phase methods. Agonist analogues will be tested in vivo and in vitro for effects on growth hormone release and in vivo for effects on basal and arginine-stimulated insulin and glucagon release and gastric acid release in the cat. In addition, effects on electrically-induced contractions of the mouse vas deferens will be examined. Antagonists can be tested in most of the above systems for inhibition of the effects of either endogenous or administered somatostatin, although the in vitro growth hormone and vas deferens systems are ideal for initial screening purposes.